The proposed research will investigate the methods of maintenance of the integrity of the chromosome. There are a number of environmental factors which may alter the functions of a cell, either by interfering with a specific pathway of metabolism or by altering or damaging the cell's content of information, the genome, producing mutagenesis. Among these are short wavelength irradiation and chemical agents which alter the structure of DNA. The purpose of this research will be to investigate protective mechanisms of biology of the cell used in response to such insult. The role of cell repair functions in mutagenesis and carcinogenesis will also be studied. Experiments will be done in an in vitro bacterial system capable of repair synthesis of DNA to study mechanisms responsible for the preservation of the message. Repair synthesis in toluene-treated E. coli is available to small molecules as well as macromolecules. This affords control over many enzymatic reactions occurring during repair. This system also offers the advantage of isolation of the intermediates and products of repair synthesis under conditions of regulated metabolism. Efforts will be directed towards extending the work to include development of an open or lysate system that will afford greater definition and macromolecular access. A direct evaluation of repair steps in repair-deficient and eukaryotes will be done. The mechanism of action of drugs such as the anti-tumor agent, Bleomycin, can be investigated to advantage in vitro. Mutants defective in repair processes can be used to define the required steps of repair in response to this agent. This agent will also be tested for mutagenicity. It will be a prototypic agent for evaluating the relationship of repair and carcinogenesis in tissue culture. The combination of genetic and molecular techniques should allow us to correlate processes occurring in vitro to those in vivo and define a common series of events that are of importance for maintenance of the chromosome in procaryotes and more complex organisms.